In one type of power and free conveyor system, the carriers are moved along a track and are adapted to be interengaged by pushers of a conveyor. It is often desirable that the carriers moving along a portion of the track be able to accumulate when they encounter a preceding carrier, an obstacle or a stop. In such conveyor systems, the carriers are returned to their original position for reuse and it is also desirable to be able to accumulate the carriers during their return as well. In one type of system, carriers are moved along an upper run of a track and returned along a lower run. Accumulation is achieved by spring pusher dogs which are difficult to adjust and maintain.
Accordingly, among the objectives of the present invention are to provide a power and free conveyor system wherein accumulation can be achieved both during the carrying portion of a track and the return portion of the track; which system is relatively simple and inexpensive to manufacture and maintain; which does not require adjustment; which will not get out of adjustment; which does not require springs, wherein the accumulation is not affected by the weight of the load and which has minimal wear.
In accordance with the invention, each carrier has a first pusher dog thereon movable downwardly when the carrier moves along the upper run for engagement with a pusher of a conveyor, and movable out of engagement with the pusher of the conveyor when the carrier moves along the lower run. The carrier has a second pusher dog thereon which is normally out of engagement with the pusher of the conveyor when the carrier is moved along the upper run and is moved into engagement with the pusher of the conveyor when the carrier is moved along the lower run. Each dog is operable upon engagement with an obstacle for movement out of engagement with the pusher of the first conveyor.